Effect Of Microbial Aggregation State On Nitrous Oxide Emission In Simultaneous Nitrification And Denitrification Nitrogen Removal Process

Simultaneous nitrification and denitrification was a novel biological nitrogenremoval process, which had advantages of saving carbon sources, low oxygenconsumption, easy control and efficient nitrogen removal. But because the operatingconditions of SND process was strict, made the nitrifiers and denitrifiers in the systemwere in a kind of "stress" condition, greatly increased the possibility of N₂O release.This study used homemade air lift circulation bioreactors to establish SND process viaselection pressure method, and studied the effect of aggregation state on N₂O releasefeatures during SND nitrogen removal process.Firstly, screened the aggregates in SND system by the particle size, and study thecharacteristics of nitrogen removal and N₂O emission. The result showed thataggregation state was the main reason led to different N₂O release. Based ontheoretical analysis and evaluating the nitrification/denitrification activity of differentmicrobial aggregates through key enzyme action ratio to select the optimalaggregation state. According to the result, when the aggregate size and density wasmoderate, can obtain higher nitrification/denitrification activity, keep the high SNDefficiency （70%）, and realize N₂O emission reduction. Compared to control, N₂Oemission reduction can be more than32.55%.Secondly, in order to study the effect of aggregation state on SND nitrogenremoval efficiency and N₂O emission, glucose and starch was introduced to be a solocarbon source of SND process. Physical and chemical indexes used to test andanalysis the aggregate structure. The results showed that both glucose and starch canbe a solo carbon source to domesticated big aggregates, but two kind of aggregateshad different appearance and structure. Aggregates which used glucose as carbonsources, was spherical. Although the size was smaller, the aggregate had denserstructure and good settle performance. Aggregates which used starch as carbonsources, the surface had a lot of filamentous, and the shape was radiate. Although thesize was larger, the structure was loose, EPS content was higher and get bad settleperformance. Synthesized the physical and chemical indexes of two types of aggregates, the aggregation state in SND can be defined four different state.Finally, investigate the nitrogen removal performance and N₂O emissioncharacteristics of two kinds of aggregates. The results showed that different carbonsource had effect on aggregate structure, and caused different nitrogen removalperformance and N₂O release characteristics. When using glucose as carbon source,the main intermediate product of SND was nitrate. Good nitrogen removal efficiencyand low N₂O emission amount in the system, and good performance can bemaintained during long term operation. When using starch as carbon source, the mainintermediate product of SND was nitrite. Nitrogen removal efficiency was poorer, andlarger N₂O emission amount was found. At the later period, sludge bulking led toseriously decline of reactor performances. Although the performances of two reactorswere different, both of the two types of aggregates had optimal aggregation state,which can realize high efficiency nitrogen removal and N₂O reduction. When usedglucose as carbon sources, the optimal aggregation state was presented at stage Ⅲ（average diameter was350⁴00μm, average specific gravity was1.17¹.18）. Atthis time, ammonia nitrogen removal efficiency was100%, total nitrogen removalefficiency was more than75%, SND efficiency was over70%, and the N₂O emissionamount maintained at the level of6⁸mgN. When the average diameter ofaggregates was450⁵00μm and average specific gravity was1.04¹.05in reacter fedwith starch, ammonia nitrogen removal efficiency reached100%, total nitrogenremoval efficiency was more than55%, SND efficiency was over60%, and the N₂Oemission amount maintained at the level of24³0mgN.